A prior art vibration control apparatus using two piezoelectric elements is illustrated in FIG. 1.
In FIG 1, vibrator 4 comprises drive piezoelectric element 2 and feedback piezoelectric element 3 which are both adhered onto one surface of vibration member 1. The output of drive apparatus 5 is supplied directly to drive piezoelectric element 2 while the output of feedback piezoelectric element 3 is fed back directly to drive apparatus 5 so as to form a vibration control apparatus that provides a constantly stabilized self-induced vibration to vibrator 4.
With prior technology of this sort, the work of assembling vibrator 4 is troublesome because it is necessary to adhere at least the drive and feedback piezoelectric elements 2 and 3 to vibration member 1. In addition, the vibration created by drive piezoelectric element 2 is transmitted to vibration member 1 via adhesive layer 6 used for the piezoelectric element 2, after which feedback output is provided through adhesive layer 7 used for feedback piezoelectric element 3. This leads to problems of unstable vibration in vibrator 4 because it is easily affected by the characteristic differences between these two piezoelectric elements 2 and 3 and by the temperature dependence of these adhesive layers 6 and 7.
It is an object of the present invention to effectively resolve such problems of prior technology by providing a vibration control apparatus that is simple to assemble and is capable of providing a constantly stabilized self-induced vibration to the vibrator.
An important application of a vibration control apparatus of the type discussed above is to a vibration gyroscope or gyro. Prior art vibration gyros which incorporate vibration control apparatus are shown as block diagrams in FIG. 2 and FIG. 3.
The vibration gyro shown in FIG. 2 comprises drive piezoelectric element 8 adhered to a first surface of vibration member 1 that is rectangular in cross-section, with feedback piezoelectric element 9 adhered to the surface opposite the first surface. The detector piezoelectric elements 10 and 11 are adhered to two more surfaces at right angles to the others to make vibrator 4. By supplying output from drive apparatus 5 to drive piezoelectric element 8 while feeding back output from feedback piezoelectric element 9 to drive apparatus 5, vibrator 4 gives a prescribed self-induced vibration in the direction of axis X in an orthogonal three-dimensional coordinate system.
Under such self-induced vibration, when vibrator 4 is rotated around axis Z, vibration is induced in the Y axis direction by the Coriolis force, and voltages accompanying this vibration in the Y axis direction are formed respectively in detection piezoelectric elements 10 and 11. These voltages are transmitted successively through differential amplifier 12, synchronous detector 13 and direct current amplifier 14 so as to obtain an indication of the angular velocity of vibrator 4 as the output of the amplifier 14.
An alternative prior art vibration gyro is illustrated in FIG. 3. The vibration gyro shown in FIG. 3 includes vibrator 4 for self-induced vibration in the X axis direction. This vibration is driven by the drive piezoelectric elements 15 and 16 which are adhered respectively to two surfaces of vibration member 1 that is triangular in cross-section. The feedback piezoelectric element 17 is adhered to another surface. The output from feedback piezoelectric element 17 is fed to drive apparatus 5. The feedback piezoelectric element 17 controls the output from drive apparatus 5 to drive piezoelectric elements 15 and 16 respectively via resistances 18 and 19. The drive piezoelectric elements 15 and 16 also serve as detection piezoelectric elements. The voltages formed by the piezoelectric elements 15 and 16 are differentially amplified by the differential amplifier 12. The output of the differential amplifier 12 is processed by the synchronous detector 13 and amplified by the D.C. amplifier 14. At the output of the amplifier 14, it is possible to detect the Coriolis force in the Y axis direction generated by vibrator 4 being rotated around axis Z, that is, to detect the angular velocity.
With the vibration gyro shown in FIG. 2, the respective piezoelectric elements 8, 9, 10 and 11 are all adhered to vibration member 1 by epoxy resin or other adhesives, creating problems in lack of stability in the self-induced vibration of vibrator 4 because of variations in vibration conditions caused by changes in the strength, elasticity and other properties of the adhesives brought about by changes, for example, in ambient temperature. Such problems may also result from the characteristic differences between drive piezoelectric element 8 and feedback piezoelectric element 9. There are also problems of variations in adhesive properties over time that cause hysteresis in drive conditions, and problems originating from variations in adhesive strength of the detection piezoelectric elements 10 and 11.
Also, variations in the properties of the several piezoelectric elements 8, 9, 10 and 11 and asymmetry in the sectional shape of vibration member 1 cause so-called offset voltages to occur because vibration in the Y axis direction, that does not occur ideally when vibrator 4 is not rotating, does occur in actuality. The size and other features of this offset voltage also change depending on the drive voltage and other drive conditions.
Also in the case of this prior technology it is necessary to adhere each piezoelectric element to each surface of vibration member 1 with high precision, causing troublesome problems in assembly labor for vibrator 4.
With the prior technology shown in FIG. 3, drive piezoelectric elements 15 and 16 are also used as detection piezoelectric elements, making it possible to decrease the changes in offset voltage brought about by changes in the adhesive under the prior technology shown in FIG. 2. However, even with this prior technology there still remains problems similar to those described above relative to vibration conditions because feedback piezoelectric element 17 is still furnished separately in the same manner as in FIG. 2.
It is a further object of the present invention to resolve such problems of prior technology by providing a vibration gyro that makes vibrator assembly work easy, and that is capable of effectively decreasing variations in drive conditions from the effect of adhesives and capable of controlling changes in offset voltages to a satisfactorily small level.